The throttle mechanism used in a camera has a mechanical configuration, and its miniaturization is limited. For example, it is difficult to produce a throttle mechanism having a diameter of 10 mm or less and a thickness of 1 mm or less as a conventional small throttle mechanism, and an ultra-small throttle mechanism having a simple structure is strongly desired that can respond to further miniaturization and reduction of weight for a small information terminal equipped with a camera such as the recent cellular phone equipped with a camera.
A piezoelectric element and a voice coil may be used as driving sources of the throttle mechanism. However, the volume change of the piezoelectric element is limited, and application of a high voltage is necessary. Further, the voice coil has a complicated structure and a large number of components and is heavy, and therefore, its miniaturization is limited.
The present inventors have been broadly examining and investigating the usefulness and application of the polymer actuator. An ion conductive actuator having an ion exchange resin layer and metal electrode layers that are formed on the surfaces of this ion exchange resin layer in an insulated state from each other is known as this polymer actuator (Patent Document 1). This polymer actuator functions as an actuator by application of a potential difference between the metal electrode layers and generating curvature and deformation in the ion exchange resin layer.
Further, a polymer actuator using a conductive polymer is known. Because this actuator is light, the total weight of devices in which it is incorporated can be reduced, and this actuator is expected to be used not only in small driving devices such as a micro machine but also in large driving devices. The actuator is expected to be applied especially to an artificial muscle, a robot arm, an artificial hand, an actuator, and the like. For example, a polymer actuator that uses polypyrrole can exhibit a maximum stretching ratio of 15.1% per one oxidation reduction cycle due to electrolytic stretching, and can generate a force of 22 MPa at maximum (for example, refer to Non-Patent Document 1).
Patent Document 1: Japanese Patent Application Laid-Open No. 2006-172635
Non-Patent Document 1: Susumu Hara and 4 others, “Highly Stretchable and Powerful Polypyrrole Linear Actuators,” Chemistry Letters, Japan, Published by the Chemical Society of Japan, 2003, Vol. 32, No. 7, pp. 576-577.